Method of interconnecting electrodes, especially carbon and graphite electrodes for electric furnaces



April 9, 1963 E. DOETSCH ETAL 3,084,419

METHOD OF INTERCONNECTING ELECTRODES, ESPECIALLY CARBON AND GRAPHITE ELECTRODES FOR ELECTRIC FURNACES Filed July 20, 1959 2 Sheets-Sheet 1 FIG. I 2

o. b f w FIG. 3

INVENTORS ERNST DOETSCH GREGOR KLI ER April 9, 1963 E. DOETSCH ETAL 3,084,419

METHOD ONNECTING ELECTRODES, ESFECI Y CARBON FIG.

United States Patent 3,084,419 Patented Apr. 9, 1963 3,084,419 METHOD OF ENTERCONNECTING ELECTRQDES,

ESPECHALLY CARBQN AND GRAPHETE ELEC- TRODES FfiR ELEQTRKI FURNAES Ernst Doetsch, Thorner Strasse 21, Nurnberg, Germany, and Gregor filler, Schwaiger Strasse 26E, Rothenbach an der Pegnitz, Germany Filed July 20, 1959, Ser. No. 828,3il2 (Ilaims priority, application Germany Oct. 4, 1953 3 (llaims. (6i. 29'--15$.5)

The present invention relates to a screw nipple connection and, more particularly, concerns a method of interconnecting by means of a screw nipple electrodes of carbon and graphite, especially for electric furnaces, to prevent accidental loosening of such connection.

For securing a screw nipple connection of the above mentioned type, the following methods have heretofore been employed. Prior to screwing in the nipple, the latter has been coated with one of the known cements or binders on a tar, pitch, resin or water glass basis. When the binder or cement is heated, it cokes and the thus formed coke is supposed non-detachably to interconnect the nipple and the nipple box forming a part of the electrodes to be interconnected, and furthermore to reduce the electric transfer resistance. With small electrode dimensions, this method has proved successful when the furnace conditions are favorable. However, with large electrodes, the difficulties will even increase for obvious reasons because the binder or cement layer between the threads shrinks during the drying and coking of said binder or cement. Even though this shrinking amounts to a few tenths of a millimeter only in the individual threads, these amounts or clearances add up. Due to the high weight of the electrode, the nipple is pulled downwardly, the end faces spread, and the current is forced to follow a path through the electrode boxes into the nipple. As a result thereof, due to the elimination of the end faces as contact surfaces, the nipple will be overloaded by approximately three times its normal load.

According to another heretofore known method, the nipple or box of the electrode is entirely or partially impregnated with tar or pitch. When subjected to heat, these inserted means sweat out and are supposed to seal the thread surfaces. This method has proved successful in many instances but, under certain furnace conditions, it has the drawback, particularly when the electrode is too quickly adjusted, that the impregnating means cts as liquid lubricant and thus directly favors the loosening of the connection if it does not coke at the proper time. The same situation is encountered when employing tar pins. In such an instance, the nipple is additionally weakened by large bores. This disadvantage is also encountered with rneltable carbon containing substances in cavities of the ends of the electrodes or the nipple.

According to another frequently practiced procedure, the screw nipple connection is secured by means of graphite pins which are driven laterally through the box into the nipple into pre-drilied bores thereof. However, ex erience has shown that the tensions caused by the graphite pins which are subjected to high tensional stress bring about'tears in the electrode box as a result of which the tension of the entire threaded box is loosened thereby unavoidably causing a loosening of the thread portion.

It is, therefore, an object of the present invention to provide a method of interconnecting electrodes of carbon or graphite by means of a screw nipple in such a way that the above outlined drawbacks will be avoided.

It is also an object of this invention to provide a method of interconnecting electrodes of carbon or graphite by means of a screw nipple and a binding substance,

in which the binding substance will be prevented from detaching itself from the electrode walls.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIG. 1 represents a longitudinal section through a screw nipple connection effected in conformity with the method of the present invention.

FIG. 2 is a longitudinal section similar to that of FIG. 1 through a modified screw nipple connection made according to the present invention.

FIG. 3 is an end face of the bottom of the threaded bore in one of the electrodes.

FIG. 4 is a longitudinal section through a modified screw nipple connection made in conformity with the method of the present invention.

FIG. 5 is a section along the line VV of FIG. 4.

General Arrangement For interconnecting electrodes of carbon or graphite for electric furnaces by means of a screw nipple, the method of the present invention prior to screwing together the nipple and electrodes, suggests to directly deposit self-hardening binding substance upon the bottom of the threaded bore in the electrode for receiving the nipple and in grooves of the nipple interrupting the thread thereof, whereupon the thus deposited binding substance will, during the screw together of the electrodes and nipple, be pressed at high pressure into all provided hollow spaces or gaps. As binding substance, a cement material on a water glass or synthetic resin basis, which will harden by itself and will not soften any more prior to the coking, has proved highly successful for the purpose involved in the present case. If desired, the binding material may have added thereto metals or metal carbides and/ or a gas driving means such as ammonium bicarbonate. The addition of metals or metal carbides to the cement substance will improve the electric conductivity of the binding substance. After the binding substance has hardened, a relative rotation of the electrodes and the screw nipple will not be possible.

Structural Arrangement Referring now to the drawing in detail, the screw nipple connection shown in FIG. 1 comprises an electrode a and an electrode [1 which are interconnected by a conical screw nipple c. The end faces of the screw nipple c and the bottom of the threaded bores in the electrodes at and b are provided with a plurality of cylindrical depressions d. Prior to screwing the parts a, b and 0 together, binding material of the character referred to above is placed upon the bottom 0 of the threaded bore p of the lower electrode b (for the sake of clarity no binding material being shown on said bottom 0). The nipple c is then firmly screwed into the bore 2. Furthermore, binding material is placed upon the top q of the nipple c and finally the electrode a is firmly screwed onto the nipple c. When screwing together the electrodes, the binding material is firmly compressed and subjected to a high pressure whereby the binding material is pressed oil into all gaps between the nipple ends and the respective adjacent bottoms of the bores p and s in the electrodes. The binding material will naturally also enter and fill the depressions 0! so that a relative rotation of the elements a, b and c relative to each other will not be possible after the binding substance has hardened.

The arrangement of FIG. 2 differs from that of FIG. 1 merely in that the depressions d of FIG. 1 have been replaced by semi-spherical depressions d.

FIG. 3 shows the end face of the screw nipple with the depressions d.

ace-gate According to the arrangement of FIG. 4, this arrangement differs from that of FIG. 2 merely in that the thread of the nipple and the thread of the bores p and s are provided with a plurality of longitudinal grooves h which communicate with the space between the end faces of the nipple and the respective adjacent bottoms of the bores p and s and are likewise filled with cement material. It will be appreciated that if a corresponding quantity of binding substance is placed upon the bottom and the top end face of the nipple c and when screwing together the parts a, I) and c, a portion of the bind ing substance will flow into the said longitudinal grooves. The said grooves h in the nipple thread and the thread of the bores should preferably be so that they will face each other when the various parts are properly screwed together. This is not difficult to obtain because, as mentioned before first the lower part of the nipple is screwed into the lower electrode so that the upper grooves in the nipple, which are preferably in alignment with the lower grooves, are visible, and can be brought into alignment with a marking on the lower electrode indicating the location of the respective grooves in the bore p of the lower electrode. The upper electrode can likewise be provided with a marking which will register with the marking on the lower electrode when the groove in the bore of the upper electrode registers with the adjacent groove in the nipple.

Experience has shown that with smaller electrode di- 'mensions, it will be fully sufficient to use either only the grooves 11 or the depressions d, d. In other words with smaller dimensions of the electrodes, the arrangement of FIG. 1 is fully suflicient. With such smaller dimensions of the electrodes, also the arrangement of FIG. 4 without the depressions d therein will sufiice.

With increasing diameter and Weight of the electrodes, the arrangement of FIG. 4 has proved highly satisfactory. In some instances, it will also suffice to introduce the binding substance merely between a smooth bottom of the threaded bores in the electrodes and the end faces of the nipple since a portion of the substance will enter the gaps between the threads.

When determining which of the various modifications is to be employed, naturally local conditions of the individual arc furnaces have to be considered. It is a wellknown fact that some furnaces operate nearly vibrationfree whereas other furnaces of the same size vibrate strongly when under high load.

It is, of course, to be understood that the present invention is, by no means, limited to the particular methods described in connection with the drawings but also comprises any modifications within the scope of the appended claims.

While various self-hardening binding cements may be employed for the above purpose, a binding cement composed primarily of graphite powder and synthetic resin and made by the company C. Conradty, Nurnberg, Germany, has proved highly satisfactory.

What we claim is:

l. A method of preventing relative rotation between two electrodes made of a material selected from the group consisting of carbon and graphite, each of which electrodes is provided with a threaded bore, and a threaded nipple threadedly engaging said bores for interconnecting said electrodes, which includes the steps of providing recesses in the bottom surfaces of the threaded bores of said electrodes and in the end surfaces of said nipple, shortly prior to interconnecting said electrodes by said nipple depositing self hardening cement material on the bottom surface of the threaded bore of one of said electrodes, screwing under pressure one portion of said threaded nipple into that bore which has cement material deposited on the bottom surface thereof so as to subject said cement material to considerable pressure to till the space between the bottom surface of said last mentioned bore and the adjacent end face of said nipple and also the recesses in said last mentioned bottom surface and said last mentioned end face, depositing additional self hardening cement material on the free end face of said nipple, screwing under pressure the other electrode on said nipple so as to subject said last mentioned cement material to considerable pressure to fill the space between said free end face of said nipple and the bottom surface of the threaded bore of said other electrode and also the recesses in said free end face and in the bottom surface of the bore of said other electrode.

2. A method of preventing relative rotation between two electrodes made of a material selected from the group consisting of carbon and graphite, each of which electrodes is provided with a threaded bore, and a threaded nipple threadedly engaging said bores for interconnecting said electrodes, which includes the steps of providing the peripheral end portions of said nipple and the inner peripheral portions of the threaded bores of said electrodes with grooves extending in axial direction of said nipple and said bores, the grooves of said bores and said nipple being adapted followingthe assembly of said nipple and electrodes to be moved into alignment with each other, shortly prior to the screwing of said nipple into the bore of one of said electrodes depositing self hardening cement material on the bottom of the bore of said one electrode, screwing under pressure one portion of said nipple into said mentioned bore while aligning the grooves on said one portion of the nipple with the grooves in the bore of the adjacent electrode, whereby cement material is pressed into said aligtned grooves under considerable pressure, depositing cement material on the free end surface of said nipple and screwing the other electrode upon said free end portion of said nipple under pressure while aligning the grooves of said free end portion of said nipple with each other whereby cement material is pressed into said last mentioned grooves of said nipple and said other electrode under considerable pressure.

3. A method of preventing relative rotation between two electrodes made of a material selected from the group consisting of carbon and graphite, each of which electrodes is provided with a threaded bore, and a threaded nipple threadedly engaging said bores for interconnecting said electrodes, which includes the steps of providing recesses in the bottom surfaces of the threaded bores of said electrodes and in the end surfaces of said nipple, and also providing outer peripheral end portions of said nipple and the inner peripheral portion of the bores of said electrodes with grooves extending in axial direction of said nipple and said bores, said grooves of said nipples and the grooves of the respective adjacent bores of said electrodes being adapted to be moved into alignment with each other prior to the complete interconnection of said electrodes and said nipple, shortly prior to interconnecting said electrodes by said nipple depositing self hardening cement material on the bottom surface of the threaded bore of one of said electrodes, screwing under pressure one portion of said threaded nipple into said last mentioned bore while aligning the grooves of said last mentioned bore with the grooves of the nipple portion engaged thereby, whereby cement material will till the space between the end surface of said last mentioned nipple portion and the bottom of the threaded bore engaged thereby of said one electrode and will also fill the adjacent recesses in said nipple and the bottom surface of said one electrode and furthermore the grooves in said one electrode and the adjacent nipple portion, depositing additional self hardening cement material on the free end face of said nipple, screwing under pressure the other electrode on said nipple so as to subject said last mentioned cement material to considerable pressure while aligning the grooves in said other electrode with the grooves of the adjs. ent nipple portion whereby eement material will fill the space between said free end 5 6 surface of said nipple and the bottom surface of the References Cimd in 1116 filfi Of this Patent adjacent electrode bore and will also till the adjacent UNITED STATES PATENTS recesses in said nipple and the adjacent bottom surface 2 2 D th Ma 18 1897 Of the Ctr d and bore and Will furthermore fill the 33 2 i g j 1937 grooves in said last mentioned electrode and the adjacent 5 2,596,513 ToccLGuflbfirt May 13, 1952 mPPle 3,014,119 Jorgensen Dec. 19, 1961 

1. A METHOD OF PREVENTING RELATIVE ROTATION BETWEEN TWO ELECTRODES MADE OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF CARBON AND GRAPHITE, EACH OF WHICH ELECTRODES IS PROVIDED WITH A THREADED BORE, AND A THREADED NIPPLE THREADEDLY ENGAGING SAID BORES FOR INTERCONNECTING SAID ELECTRODES, WHICH INCLUDES THE STEPS OF PROVIDING RECESSES IN THE BOTTOM SURFACES OF THE THREADED BORES OF SAID ELECTRODES AND IN THE END SURFACES OF SAID NIPPLE, SHORTLY PRIOR TO INTERCONNECTING SAID ELECTRODES BY SAID NIPPLE DEPOSITING SELF HARDENING CEMENT MATERIAL ON THE 